st: how to estout the first-stage results of -ivreg2-?

I type the following in the stata to store the first-stage results,
ivreg2 y z (x= z1 z2), savefirst savefprefix(first)
However, if I type,
eststo dir
nothing appears!
Where does stata store the first-stage results? Then I can estout them.
Thank you for any help!
Sincerely,